Titanium or tantalum base electrodes with applied titanium or tantalum oxide face activated with noble metals or noble metal oxides

ABSTRACT

Describes a titanium or tantalum base electrode having a protective and electrocatalytic layer applied to the faces exposed to the electrolyte, said protective and electrocatalytic layer consisting of mixtures of solid solutions of valve metal oxides and platinum group and noble metals as such or in the form of oxides and/or oxyhalides.

United States Patent [72] Inventors Giuseppe Blanchi Milan, Italy;Vittorio DeNora, Nassau, Bahamas; Patrizio Gallone; Antonio Nidola,Milan, Italy [21] I Appl. No. 690,407

[22] Filed Dec. 14, 1967 [45] Patented Oct. 26, 1971 [73] AssigneeElectronor Corporation Chiasso, Switzerland [54] TITANIUM OR TANTALUMBASE ELECTRODES WITH APPLIED TITANIUM OR TANTALUM OXIDE FACE ACTIVATEDWITH NOBLE METALS [50] Field of Search 204/290 F, 98, 99

[56] References Cited UNITED STATES PATENTS 2,631,115 3/1953 Fox 204/290F 2,719,797 10/1955 Rosenblatt et al.. 204/290 F 3,177,13] 4/1965 Angeliet al.....L 204/290 F FOREIGN PATENTS 6,606,302 10/ 1966 Netherlands204/290 F Primary Examiner-T. Tung Attorney-Hammond & Littell ABSTRACT:Describes a titanium or tantalum base electrode having a protective andelectrocatalytic layer applied to the faces exposed to the electrolyte,said protective and electrocatalytic layer consisting of mixtures ofsolid solutions of valve metal oxides and platinum group and noblemetals as such or in the fonn of oxides and/or oxyhalides.

TITANIUM OR TAN'IALUM BASE ELECTRODES WITI-I APPLIED TITANIUM ORTANTALUM OXIDE FACE ACTIVATED WITH NOBLE METALS OR NOBLE METAL OXIDESThis invention relates to an improvement in electrodes for use in anodicand cathodic reactions in cells used for example in the manufacture ofchlorine and caustic alkali by the electrolysis of aqueous solution ofalkali metal chlorides, for use in other processes in which anelectrolysis current is passed through an electrolyte for the purpose ofdecomposing the electrolyte, for carrying out organic oxidations andreductions and for other purposes.

The invention is particularly valuable in flowing mercury cathode cellsin which the cathode consists of mercury flowing over the cell base andin which the anodes are suspended above the flowing mercury cathode andthe electrolysis of the brine takes place in the space between theanodes and the cathode. This, however, is only one illustration of theapplication of the invention and it may be used in diaphragm cells andin all other types of electrolysis cells and-for other electrolysis andoxidation purposes.

With the advent of dimensionally stable anodes, based upon the use ofvalve metals, such as titanium, tantalum, zirconium, molybdenum andtungsten, which in service develop an oxide or barrier layer whichprevents the further flow of anodic current through the anode, except atsubstantially higher voltage, it was considered necessary to cover theentire face of the titanium or tantalum anode with a conductive layer ofnoble metal from the platinum group (i.e., platinum, palladium, iridium,osmium, rhodium, ruthenium or alloys thereof), by electroplating orotherwise, which completely covered the titanium or tantalum base,except for inevitable pores through the coating metal, which pores were,however, sealed by the development of the barrier layer above referredto on the titanium or tantalum base.

The platinum group metals are, however, expensive, good adherence andgood conduction between the titanium base and the platinum group metalcoatings is difficult to secure, the platinum group metal coatings areconsumed or lost in the electrolysis process, frequent cell shut downsare necessary to replace defective anodes, and the cost of the coating,per ton of chlorine produced, is high. Although many platinum groupmetal coated titanium base anodes have been produced and tested, noplatinum group metal coated titanium base anodes have heretofore beenproduced either by the use of coatings of platinum group metalsthemselves or by the use of oxides of such metals, which gave reliableand reproducible results and which could be produced in commercialquantities and used satisfactorily in commercial electrolysis cells.

We have found that it is not necessary to cover the metal base ofanodes, such as titanium or tantalum, with a conductive layer of aplatinum group metal over the entire surface, but that a coating made ofa valve metal oxide or oxyhalide, such as, for instance, titanium oxide,titanium oxychloride, tantalum oxide, tantalum oxychloride, zirconiumoxide or oxyfluoride, may also develop electrocatalytic properties. ifits structure is modified by the addition of platinum group and noblemetals, either as such or in the form of oxides or oxyhalide.Furthermore, we have found that the coatings so applied will give equalor greater conduction than an entire anode surface coated with platinumor a platinum group metal or oxide and that the coating so applied ismore resistant to the celloperating conditions than platinum platedanodes and will cost far less per ton of chlorine produced than theplatinumplated titanium base anodes heretofore produced. The anodes ofour invention will resist current reversals and amalgam dips, and resistthe conditions of commercial operation in an electrolytic cell betterthan anodes which have their entire active surface coated with aplatinum layer, and will produce a higher chlorine discharge with lessovervoltage and have less wear per ton of chlorine produced than theprevious anodes, completely covered with platinum group metals.

It is, therefore, an object of our invention to produce an anode for usein electrolysis processes which will have a long active life beforedeveloping an overvoltage for chlorine discharge and which will beresistive of the conditions of practical operation encountered in anelectrolysis cell.

Another object of our invention is to produce a titanium or tantalumbase anode provided with modified valve metal oxide or valve metaloxyhalide coatings which will continue to conduct electric current fromthe anode base to the electrolyte over long periods of time,without-spalling or peeling of the coating from the anode base underpractical cell conditions, and without material loss of theplatinumgroup metal conductor, in the electrolysis process. J

Another object of our invention isto provide a conductive coating on atitanium anode base which will be economical in the use of the platinumgroup and noble metals used for the coating and which will produce ahigh yield of chlorine per gram of the platinum group and noble metalsused in the anode coating, or consumed in the electrolysis process.

Another object of our invention is toproduce a titanium or tantalum baseelectrolysis anode provided with platinum group and noble metalsdissolved as such, or in the form of oxides or oxyhalide, within thevalve metal so that the platinum group and noble metals or oxides areprotected from operative cell conditions by the presence of the valvemetal'oxide which firmly adheres to the titanium or tantalum base andprotects the platinum group and noble metals from destruction by currentreversals, amalgam dips, short circuits and corrosive action of chlorinecontaining electrolyte encountered during operation of an electrolysiscell.

Another object of our invention is to provide a titanium or tantalumbase anode having a coating comprising a mixture of titanium or tantalumoxides or oxychlorides of ruthenium oxide or oxychloride and of iridiummetal, in which the weight ratio of noble metals to valve metal is notlower than 20/l00 20/100 and not higher than 85/800.

Various other objects and advantages of our invention will appear asthis description proceeds.

While any platinum group metals or alloy or oxides thereof may be used,we have secured our best results with iridium metal dissolved mixturesof ruthenium oxide or oxychloride embedded in and surrounded by atitanium or tantalum oxide or oxychloride coating applied on a titaniumor tantalum base or core, and our invention will be described withreference to this preferred embodiment, without, however, intending tolimit the invention to these embodiments.

Unlike prior platinum group metal coated titanium base anodes, whichdepend upon the development of a barrier layer of titanium oxide betweenthe pores of the platinum group metal coating, our invention provides avalve metal oxide or oxyhalide coating on the titanium basewhich coatingsurrounds and protects the platinum group metal or oxide fromdestruction and wear under operative electrolysis cell conditions.

The electrodes of our invention are particularly useful as anodes forthe electrolysis of sodium chloride brines in horizontal mercury cellsand diaphragm cells as they have the ability to liberate chlorine atlow-anode voltages essentially throughout the life of the platinumgroup'metal or oxide conductors and conductive points and have a lowwear rate (loss of noble metal per ton of chlorine produced).

Passivity of platinum or platinum group coated anodes of the prior artin electrolysis of brines has been a problem. Passivity refers to therapid rise in potential in the said anodes after being used for sometime at sufficiently high-current density under chlorine discharge. Thisrise in potential indicates that the anodic oxidation of the dissolvedchloride ion to molecular chloride gas will proceed only ata higherovervoltage because of the diminished catalytic activity of theelectrode surface.

The anodes of our invention have a lower anode potential and operate fora much longer time before reaching passivation than platinum group metalcoated anodes, which demonstrate the high activity and long life of theanodes of our invention. This is particularly advantageous inelectrolytic cells for the electrolysis of brines such as sodiumchloride since the said cells can be operated for much longer periods oftime before the electrodes have to be replaced, and shut down time ofthe cells is greatly reduced. Our invention also reduces the amount ofthe platinum group metal initially used, and eventually consumed, perton of chlorine, making the process more economical.

In addition to the platinum group metals or oxides our anodes may befurther improved by incorporating into the platinum group metal oroxides a minor amount of an activating element, such as antimony, asdescribed in the copending application U.S. Ser. No. 506,852, filed Nov.8, I965, now U.S. Pat. No. 3,428,544.

The conductive coating of our invention may be applied in various ways,and to various forms of titanium or tantalum base anodes, such as solidrolled massive titanium plates, perforated plates, slitted, reticulated,titanium plates, titanium mesh and rolled titanium mesh, woven titaniumwire, or screen or similar tantalum plates, all of which will bereferred to as mesh form." Our preferred method of application is bychemi-deposition in the form of painted on, dipped, sprayed or curtaincoatings baked on the titanium anode base, but other methods ofapplication, including electrophoretic deposition or electrodeposition,may be used.

In all applications the titanium or tantalum base must be cleaned andfree of oxide or other scale. This cleaning can be done in any way, bymechanical or chemical cleaning, such as by sand blasting, etching,pickling or the like.

EXAMPLE I An expanded titanium anode plate, with a surface of 50 cm.projected area, was cleaned by boiling at reflux temperature of l l C.in a 20 percent solution of hydrochloric acid for 40 minutes. lt wasthen given a liquid coating containing the following materials:

Ruthenium as Ru Cl,-H,0- l0 mg. (metal) Iridium as (NI-l,),lr Cl l0 mg.(metal) Titanium as TiCl 56 mg. (metal) Formamide (HCONH,)-l0 to 12drops Hydrogen peroxide (H O, 30%)-3 to 4 drops The coating was preparedby first blending or mixing the ruthenium and iridium salts containingthe required amount of Ru and Ir in a 2 molar solution of hydrochloricacid (5 ml. are sufficient for the above amounts) and allowing themixture to dry at a temperature not higher than 50C. until a dryprecipitate is formed. F Ormamide is then added to the dry salt mixtureat about 40C. to dissolve the mixture. The titanium chloride, TiCldissolved in hydrochloric acid percent strength commercial solution), isadded to the dissolved Ru-lr salt mixture and a few drops of hydrogenperoxide (30% H 0 are added, sufficient to make the solution turn fromthe blue color of the commercial solution of TiCl to a brownreddishcolor.

The coating mixture, thus prepared was applied to both sides of thecleaned titanium anode base, by brush, in eight subsequent layers. Afterapplying each layer, the anode was heated in an oven under forced aircirculation at a temperature between 300and 350C. for 10 to l5 minutes,followed by fast natural cooling in air between each of the first sevenlayers, and after the eighth layer was applied the anode was heated at450C. for l hour under forced air circulation and then cooled.

The amounts of the three metals in the coating correspond to the weightratios of [315% lr, l3'l5% Ru and 737% Ti and the amount of noble metalin the coating corresponds to 0.2 mg. lr and 0.2 mg. Ru per squarecentimeter of projected electrode area. It is believed that the improvedqualities of our anode are due to the fact that although the threemetals in the coating mixture are originally present as chlorides theyare codeposited on the titanium base in other fonns. Stoichiometricdeterminations indicate that in the final coating the iridium chlorideis reduced to metallic lr, whereas ruthenium chloride an titaniumchloride are converted into ruthenium oxide RuO, and titanium oxide oroxychloride TiOCl. ln accelerated testing, the anode of this exampleshowed a weight loss of zero after three current reversals, a loss of0.152 mgJcm. after three amalgam dips as against a weight loss of 0.93mgJcm. of a similar titanium base anode covered with ruthenium oxide.After 2,000 hours of operation this anode showed a weight increase of0.7 mg./cm., whereas similar anodes covered with a layer of platinum orruthenium oxide showed substantial weight losses. The weight increasehad apparently become stabilized.

EXAMPLE II The coating mixture was applied to a cleaned titanium anodebase of the same dimensions as in example I according to the sameprocedure. The applied mixture consisted of the following amounts:

Ru as RuCl -H,O-20 mg. (metal) lr as (NH,),lrCl,,-20 mg. (metal) Ti asTiCl,-48 mg. (metal) HCONH,- 10 to 12 drops H 0, 30 -3 to 4 drops Theprocedure for compounding the coating and applying it to the titaniumbase was the same as in example I. The quanti ties of the three metalsin this mixture corresponded to the weight ratios of 22.6 lr, 22.6 Ruand 54.8 Ti and the amount of noble metal oxide in the active coatingcorresponded to 0.4 mg. lr, and 0.4 mg. Ru per square centimeter of theactive electrode area. After 2300 hours of operation this anode showed aweight increase of 0.9 mgJcm. which had apparently become stabilized.

EXAMPLE Ill Before being coated, the titanium anode after pre-etching,as described in example I, was immersed in a solution composed of lmolar solution of H 0 1 plus a l molar solution of NaOH at 20 to 30 C.for 2 days. The surface of the titanium was thus converted to a thinlayer of black titanium oxide.

The coating mixture of the same composition as given in example l wasused, except that isopropyl alcohol was used as the solvent in place offormamide. The use of isopropyl alcohol resulted in a more uniformdistribution of the coating films on the black titanium oxide substratethen when formamide was used as the solvent.

EXAMPLE IV An expanded titanium anode plate of same size as in thefonner examples was submitted to the cleaning and etching procedure asdescribed above and then given a liquid coating containing the followingmaterials:

Ru as Rucl 'li O-- 10 mg. (metal) In as IrCl, l0 mg. (metal) Ta as TaClmg. (metal) lsopropyl alcohol-5 drops 20 l-lCl-5 ml.

The coating was prepared by first blending or mixing the ruthenium andiridium salts in 5 ml. of 20 5 HCl. The volume of this solution was thenreduced to about one-fifth by heating to a temperature of C. Therequired amount of TaCl, was dissolved in boiling 20 HCl so as to form asolution containing about 8 TaCl, by weight. The two solutions weremixed together and the overall volume reduced to about one-half byheating at 60 C. The specified quantity of isopropyl alcohol was thenadded.

The coating mixture was applied to both sides of the cleaned titaniumanode base in eight subsequent layers and following the same heating andcooling procedure as described in example I.

The amounts of the three metals in the coating correspond to the weightratios of 10 Ru, l0 lr and 80 Ta and the amount of noble metal in thecoating corresponds to 0.2 mg. Ir

area. ln accelerated testing, this anode showed a weight loss of TABLEI.ACCELERATED WEIGHT LOSS TESTS Current Amalgam 0.0207 mg./cm. afterthree current reversals and a loss of s 1 n 1 Tom 0.0138 after twoamalgam dips. After 514 hours of operation amp 6 this anode showed aweight decrease of 0.097 mg./cm. 5 A (Example I):

% St f? z 0 152 0 152 U cm. BIO EXAMPLE v Ti 1.12 cm: l

- C (Exampl I ll): An expanded titanium anode plate of same size as inthe Ru 0.2 mgJcmJ- z 0 0 0 m former examples, after cleaning andetching, was glven a T1 y g w (wk n o liquid coating containing thefollowing materials: D g g ig %9 titanium base- Ru as aucl -n o-l 1.25mg. (metal) Ir Min cut: Au as HAuCL-nH,O-3.75 mg. (metal) Ru s/ems- 0,02m 0, 013g 0345 Ta 1.6 m Jeni- Tl 8STlCl 60 mg. (metal) E (Example )z/2 0.075 .c lsprpyl 5-10 dmls l5 xiii 0.225 E g $1. Q. 030 0. 04a 0. 013H 0, 30 %-2-3 drops T1 1.2 mgJCm. The coating was prepared by firstblending the ruthenium Q2 (173 (193 and gold salts in the requiredamount in a 2 molar solution of y r h i d 11 and al g t mix u t dry at aWeight losses on samples prepared according to the present temperatureof The commercial Solution of Ticls was invention were determined undersimulated operating condi- Ih addod to the RU-All Salt miXlure and a fewdrops of tions and compared with weight losses determined under same hyr gen p xi r stirred in h solution. sufficient to conditions on titaniumbase samples coated with a Pt-lr alloy. m the Solution turn from bllloto brown feddlsh- P PY The tests were conducted in NaCl saturatedsolution at 65 C. alcohol was finally added in the required amount. Thecoating d under a di nt density of 1 A./cm. Anode mixture thus preparedwas applied to both sides of the cleaned otentials were measured bymeans of a Luggin tip against a titanium anode base in eight subsequentlayers, f llo ing the saturated calomel electrode and converted to thenormal a healing and Cooling Procedure as described in example hydrogenelectrode scale. The relevant results are summarized The amounts of thethree metals in the coating correspond in table ll. The integratedweight change, as shown in the next 10 mo Weight ratios of 15 5 80 Tiand the to last column, was positive, that is increased, for most of theamok"!t of noble metal in h Coating P I0 0225 samples prepared accordingto the present invention; this is an mg. Ru and 0.075 mg. Au per squarecentimeter of projected indication that the coating, instead ofgradually wearing off electrode area. In accelerated testing this anodeshowed a d h decreasing i precious metal content, tends to build Weigh108 of -0 rng-l r lafter three Current reversals and up an additionalamount of protective valve metal oxide which a 1 f 4 "lg/Cm after two mg m dips. After 5 l4 reaches stability after a short period of operationas shown by hours of operation this anode showed a weight change of +0.23 Sample B, mg./cm. On the contrary, the results summarized in table Ishow that Stoichiometric determinations indicate that the final even thebest noble metal alloy coatings suffer a greater wear deposit containsthe three metals in the following form: gold is rate, during operation;while such wear rate is not necessarily reduced by thermal decompositionto the metallic state Au, to be imputed exclusively to the spalling offof noble metals, it whereas ruthenium chloride and titanium chloride areconcertainly involves also a substantial decrease of the noble vertedinto ruthenium oxide RuO and titanium oxychloride metal content in thecoating. The amount of noble metals in TiOCl, respectively. such noblemetal alloy coatings, which is the amount necessa- Our tests so far haveshown that when using the fonnulary to obtain a satisfactory anodeactivity and a sufficiently long tions and deposition methods describedabove the presence of 5 operating life, is from five to ten timesgreater than in the titanium or tantalum oxide or oxychloride andiridium alone, 4 coatings prepared acggdingto the present invention.

TABLE II Wear Anode rate Coating Operatlng potential grams compositionours at volt Integrated weight per t Sample (mg/cm!) 1 AJcm. (N.H.E.)change, mgJcm. Cl:

Ir (0.2) 0 1.62 0 1A (Example-1).. R110; (Ru.0.2). 792 1.53 +0.3 (weightincreased). 0 v (Ti 1.12)... 2,003 52 +0.7 (Weight increased). 0 I B(Example 11) RuO: (Ru 0.4) 860 1.36 +0.9 (increase) 0 'llOCl (Tl 0 2,3001.38 +0.9 (increase) 0 Ir (0.2).... 0 1.50 C (Example III) R1102 (Ru 5521.44 +0.75 (increase) 0 813 +0.4 (lncrease)..... 0 D (Example 1v) R110}('1'iti'6.'2).III 514 1145 tifdsi ioiifmiseilli (l l5 TaOzCl (Ta 1.6)--Au (0.075)......... 0 1.48 E (Example V) RuOz (Ru 0.225).. 514 1.48 +0.2(increase). 0

' TlOCl (Tl 1.2) 0 1 36 F {Pt (1.44) 1,032 1143 6:23 (decree 561:: 6.55Ir (3.36).......... 2, 378 .9 (decrease) 0. G {Pt (3.68) 92s 1135 'fI1'(0.92) 2,940 1.39

Stoichionietricdeterminations indicate that the final coating containsthe three metals in different form than the startcioiis metals in thecoatings may be between 20 to 100 and 85 to 100.

While we have set forth theories as to the final composition of ourimproved electrodes we do not intend to be bound by these theories butbase our claim to invention on the procedures described to produce theseelectrodes and the results obtained in their use.

The word oxide in the following claims is intended to cover oxides oftitanium and tantalum whether in the form of Tit) and Ta or TiOCl andTaO,Cl, or other oxides of these metals and the words noble metals isintended to include the latinum group metals and gold and silver.

Various modifications and changes may be made in the steps describedwithout departing from the spirit of our invengion or the scope of thefollowing claims.

We claim:

1. An electrode comprised of a metal base from the group consisting oftitanium and tantalum having a coating thereon, the major portion ofwhich is an oxide of a valve metal from the group consisting of titaniumand tantalum and the minor portion is an oxide of ruthenium, said minorportion also containing a material from the group consisting of iridiumand gold, said coating being formed by applying onto said base asolution containing a metal compound from the group consisting of atitanium compound and a tantalum compound, a ruthenium compound and ametal compound from the group consisting of an iridium compound and agold'compound and heating the coating in air to bake said coating onsaid base.

2. The electrode of claim 1 in which the minor portion contains iridiumand the iridium is in substantially equal amounts with the metal in theruthenium oxide.

3. As a product of manufacture, a titanium base electrode in mesh formhaving a titanium oxide coating with a mixture of ruthenium oxide andone metal from the group consisting of iridium and gold extendingthrough the coating and capable of conducting current from the titaniumbase through said coating to the exposed surface of said coating, saidcoating being formed on said base from a solution containing a titaniumand a ruthenium compound and a compound from the group consisting of aniridium compound and a gold compound and baked on said base.

4. The product of claim 3 in which the metal in the ruthenium oxide andthe metal compound from the group consisting of iridium and goldconstitute from about 20 to about percent of the weight of the metal inthe titanium oxide.

5. The product of claim 3 in which the metal is iridium, said metal andthe metal in the ruthenium oxide are in approximately equal amounts andconstitute from about 20 to about 85 percent of the weight of the metalin the titanium oxide coating.

6. The product of claim 3 in which the coating is on all sides of thetitanium base electrode.

7. The product of claim 3 in which the coating is applied In a pluralityof layers and the electrode is heated in an oxidizing atmosphere aftereach layer is applied.

8. As a product of manufacture, an electrode consisting of a core ofsolid massive substantially nonporous valve metal from the groupconsisting of titanium and tantalum in mesh form, a substantiallynonporous oxide layer of the same metal on said core in mixture withruthenium oxide and a metal from the group consisting of iridium andgold, said layer being formed by applying a solution containing acompound from the group consisting of a titanium compound and a tantalumcompound, a ruthenium compound and a compound selected from the groupconsisting of an iridium compound and a gold compound onto said core andbaking on said core.

9. The product of claim 8 in which the oxide from the group consistingof titanium and tantalum oxides, the ruthenium oxide and the metal fromthe group consisting of iridium and gold are mixed together as chlorideand applied to the core and baked on the core under air circulation.

10. As a product of manufacture, an electrode comprising a core oftitanium and a conducting cover coating over said core consisting of (a)titanium oxide, (b) ruthenium oxide and (c) a metal from the groupconsisting of iridium and gold, said coating being formed by applying asolution containing a titanium compound, a ruthenium compound and acompound from the group consisting of an iridium compound and a goldcompound onto said core and baking thereon, said coating being inmultiple layers on said core and the metal in the titanium compoundconstituting more than 50 percent of the weight of the metals in saidcoating.

2. The electrode of claim 1 in which the minor portion contains iridiumand the iridium is in substantially equal amounts with the metal in theruthenium oxide.
 3. As a product of manufacture, a titanium baseelectrode in mesh form having a titanium oxide coating with a mixture ofruthenium oxide and one metal from the group consisting of iridium andgold extending through the coating and capable of conducting currentfrom the titanium base through said coating to the exposed surface ofsaid coating, said coating being formed on said base from a solutioncontaining a titanium and a ruthenium compound and a compound from thegroup consisting of an iridium compound and a gold compound and baked onsaid base.
 4. The product of claim 3 in which the metal in the rutheniumoxide and the metal compound from the group consisting of iridium andgold constitute from about 20 to about 85 percent of the weight of themetal in the titanium oxide.
 5. The product of claim 3 in which themetal is iridium, said metal and the metal in the ruthenium oxide are inapproximately equal amounts and constitute from about 20 to about 85percent of the weight of the metal in the titanium oxide coating.
 6. Theproduct of claim 3 in which the coating is on all sides of the titaniumbase electrode.
 7. The product of claim 3 in which the coating isapplied in a plurality of layers and the electrode is heated in anoxidizing atmosphere after each layer is applied.
 8. As a product ofmanufacture, an electrode consisting of a core of solid massivesubstantially nonporous valve metal from the group consisting oftitanium and tantalum in mesh form, a substantially nonporous oxidelayer of the same metal on said core in mixture with ruthenium oxide anda metal from the group consisting of iridium and gold, said layer beingformed by applying a solution containing a compound from the groupconsisting of a titanium compound and a tantalum compound, a rutheniumcompound and a compound selected from the group consisting of an iridiumcompound and a gold compound onto said core and baking on said core. 9.The product of claim 8 in which the oxide from the group consisting oftitanium and tantalum oxides, the ruthenium oxide and the metal from thegroup consisting of iridium and gold are mixed together as chloride andapplied to the core and baked on the core under air circulation.
 10. Asa product of manufacture, an electrode comprising a core of titanium anda conducting cover coating over said core consisting of (a) titaniumoxide, (b) ruthenium oxide and (c) a metal from the group consisting ofiridium and gold, said coating being formed by applying a solutioncontaining a titanium compound, a ruthenium compound and a compound fromthe group consisting of an iridium compound and a gold compound ontosaid core and baking thereon, said coating being in multiple layers onsaid core and the metal in the titanium compound constituting more than50 percent of the weight of the metals in said coating.